I am currently a postdoctoral fellow in Dr. Klaus Kaestner's laboratory in the Department of Genetics, at University of Pennsylvania. My previous Ph.D. and postdoctoral training experience has been continuously related to gut endoderm development. My immediate goal during the next 3 years is to complete the transition to an independent scientist in the field of gastrointestinal development and diseases. My long-term goal is to investigate the cell polarity regulators and their roles in the gastrointestinal morphogenesis and related diseases. I am working in a very dynamic research environment that has highly interactive scientists from the Department of Genetics, the Gastroenterology Division and the Institute for Diabetes, Obesity and Metabolic Diseases. Dr. Klaus Kaestner will be my primary mentor, and Dr. Anil Rustgi, the Chief of Gastroenterology Division, will be my co-mentor. Dr. Kaestner is an expert in mouse genetics and gut development. Dr. Rustgi is a well-respected expert in gastrointestinal development and diseases. Both mentors have ample experiences in training young scientists and have a track record of successful mentoring and transitioning K awardees into independent faculties. Other key advisors include Dr. Erfei Bi, an expert in Cdc42 and cell polarity research, Dr. Michael Pack, an expert of Zebrafish gut development, and Dr. Hiroshi Nakagawa, an expert in primary tissue culture and organotypic culture model. Two technical consultants, Drs Jonathan Schug and Raymond Meade, will advise me on statistical data analysis and EM experiments. The mammalian intestine contains a highly polarized epithelium that is central to digestion and absorption of nutrients. Although we have ample knowledge about canonical Wnt, Notch and other signaling pathways in the intestinal epithelial morphogenesis, little is known about the roles of key polarity regulators in this process. Several cell polarity genes have been implicated in gastrointestinal diseases, in particular the colon cancer. My recent work with Dr. Kaestner has established Cdx2 as the essential intestinal cell fate director. This work has been accepted by Developmental Cell. Our preliminary data on intestinal epithelium-specific Cdx2 knockout mice suggest that this factor plays an important role in regulating cell polarity formation in differentiated intestinal epithelium, and this effect appears to be associated with the apical Par complex and Cdc42 polarity pathways. Ablation of Cdx2 from differentiated intestinal epithelium leads to a disrupted apical-basolateral cell orientation, an extra tight junction formation, and an impaired basement membrane integrity. We hypothesize that apical polarity complex (Par3/Par6/aPKc/Cdc42) incorporates intestinal cell lineage information to instruct polarity formation during epithelial morphogenesis. We propose to analyze the spatial and temporal activity of Par/aPKC and Cdc42 during normal intestinal polarization, and investigate the molecular mechanism by which Cdx2 regulates apical polarity activation during the morphogenetic process. We will further define the role of Cdc42, a master regulator of cell polarity, in the development of intestine, using a novel intestinal organotypic culture model, in combination with the intestine-specific Cdc42 knockout mouse model. These studies will elucidate the basic mechanisms of cell polarity regulation in mammalian epithelial morphogenesis, and will contribute to a better understanding of related gastrointestinal diseases. The goal of this proposal is directly relevant to the mission of NIDDK. The training process will expand my technical capacities such as the development of a novel intestinal organotypic culture model, and the utilization of immuno-electron microscopic analysis to localize polarity regulators during intestinal morphogenesis. The award will protect my time for generating new genetic models including the intestine-specific Cdc42 knockout mice.